Steam-pressure gage



PATENTED JUNE 16, 1857.

J. L.-EASTMA-N.

STEAM PRESSURE GAGE.

UNITED STATES PATENT OFFICE.

JOSEPH L. EASTMAN, OF BOSTON, MASSACHUSETTS.

STEAM-PRESSURE GAGE.

Specification of Letters Patent No. 17,560, dated. June 16, 1857.

T 0 all whom it may concern:

Be it known that. I, JOSEPH L. EASTMAN, of Boston, in the county of Suffolk and State of Massachusetts, have invented a new and useful Improvement on Pressure-Gages; and I do hereby declare that the following is a full, clear, and exact description of the construction and operation of the same, reference being had to the annexed drawings, making a part of this specification, in which Figure I, is a front view of the instrument with a portion of the dial plate removed,

and Fig. II is a side view of the lower part of the interior of same.

My improved gage is adapted, among other things, to indicate, in pounds a-voirdupois, the pressure, above that of the at mosphere, upon each square inch of the in terior of a steam boiler.

That class of pressure gages for steam boilers in which the pressure of the steam is measured by the force it exerts in lifting a weight or bending a spring, consists of several divisions, each of which has its own special merits and disadvantages. Three of these divisions, towhich my improvements relate, I will describe briefly, in order that the nature and scope of my invention may be better understood. In the first of these divisions a piston is fitted into a small aperture in the boiler,in such manner that the full pressure of the steam will bear upon the inner end of the piston and tend to force it out of the aperture. To prevent the piston from being thus forced out and at the same time to gage the force exerted to push it out, its outer end is connected to a spring balance, which constantly tends to push the piston into the aperture, so that when the pressure within the boiler increases the balance will be compressed as by an increase of weight in the scale-pan, which increase will be denoted by the index of the balance, and when the pressure within the boiler diminishes, the reverse of this operation will take place and the diminished pressure will be correctly denoted by the index. Such is the theory of the action of the piston and spring gage, but its practicaloperation is far different, for the piston, however accurately it maybe fitted, will at some times work so loosely and at other times so tightly in the aperture, as to be pushed out to widely different distances by the same degree of pressure within the boiler, and this destroys all reliability in its indications and renders this division of gages practically worthless. In the second division of these gages the piston and spring were replaced by means of an elastic diaphragm confined by its edges over the aperture, with a disk, nearly as large as the aperture, resting upon the diaphragm, and a weighted lever pressing upon the disk and tending continually to press the diaphragm down upon the aperture. The pressure within the boiler causes the diaphragm to bulge outward, but, by reason of its elasticity, it resists this bulging out, with a 'force which increases with the pressure,

which elastic force, together with the weight bearing upon the disk, constitutes the resistance to the pressure of the steam and the distance which the long end of the weighted lever moves over a graduated scale indicates the amount of pressure within the boiler. These indications of pressure are found to be unreliable because ofthe varying elasticity of the diaphragm from variations of temperature and the rapid diminution of its elastic force, from the straining produced by the wide range of motion which, in these gages, must necessarily be given to it. From these causes this division of gages is without practical value. In the third di vision of these gages, the defects of the second were remedied, so far as they resulted from giving too wide a range of motion to the diaphragm and from deriving the compensating force for the variable pressures in the boiler, from the elasticity of the diaphragm itself, by making the diaphragm so thin it would be very flexible and its resistance to bulging very slight, and, by means of a compensating lever of variable length and a weighted lever with a variable fulcrum and acting with variable force upon the compensating lever, so as to increase the resistance of the disk rapidly as the diaphragm bulges outward from an increase of pressure within the boiler, and so stantly in the use of such instruments, this division of gages is not only difficult to con-.

struct but it is still more difficult to maintain in them a compensation sufliciently perfeet to render their indications of pressure sufficiently reliable for practical use. But these gages have another and a still greater defect: The 'compei'isating weight must be comparatively heavy, its range of motion considerable and its movements COIIGSDOIKI- ingly rapid. The rapid motion of the weight creates a degree of momentum which raises it far beyond the point to which the increase of pressure would lift it and depresses it below the point due to a diminution of pressure, and, as the pressure within a steam boiler is constantly and rapidly changing, from the frequent opening of the valves to supply the engine and the rapid generation of steam in the intervals between the opening of the valves, this weight, in this division of gages, is kept in a state of rapid vibration which precludes any indi cation of the actual or maximum or minimum pressure in the boiler, and further;-if such a gage is placed upon a marine or 1600- motive steam-boiler the motion of the vessel in the one case and that of the locomotive in the other, swings the weight so as to disturb its pressure upon the diaphragm and thus disturbs the indications of the pressure within the boiler. From these causes this division of gages is not sufficiently ac curate and reliable in indicating the pressure within a steam boiler.

It is the purpose of my invention to combine the advantages of the several divisions of gages just described and, at the same time, to avoid their disadvantages, not by constructing a gage upon an entirely new principle or adding to this class of gages any new element, but, by a new combination of elements well known in gages, constituting a new division of the class, more accurate and reliable than those which comprise other and differentcombinations; and my improvement consists in combining with an elastic diaphragm over an aperture in or communicating with the interior of a steam boiler, a disk bearing upon the diaphragm and held down by a multiplying lever, which, in turn, is held down by a compensating spring; the lever being connected with an index moving over a dial-plate graduated into equal divisions or thereabout and over which the index moves an equal distance for any given increase or diminution of pressure. This gage is practically unatfected'by the jarring motion of a locomotive or steamboat; involves no uicety or difiiculty of construction; is not liable to derangement, and, from the very slight movement in the diaphragm toindicate the ex tremes' of pressure, this element of the gage seems to be as durable as any other part, as,

after nearly two years of experimental use on a locomotive and repeated and most severe tests, it does not appear to be in the least degree impaired.

In the annexed drawings (Figs. I and II) A, represents the pipe or tube leading from the steam-boiler to the lower part of the gage, which it enters by a hole B, made in the side of the case C, D, E, F. The pipe A, is screwed into a piece of iron, shown at G, through which there is an aperture, which may be of the same size the steam-pipe, or it may be enlarged at the part farthest from the pipe, marked H. A piece of vulcanized sheet india-rubber I, is placed upon this aperture, and extends a short distance upon each side of it, being held firmly in contact with the iron plate G by means of the cap-piece J, and the bolts and nuts K K. In the cap-piece J, there is an aperture L, which is placed directly opposite to the opening H, above described, and having its area where it joins the sheet rubber I, about equal to the area of the openings at H.

Vithin the aperture L, and in contact with the rubber, I place a metallic disk M, of less area than the openings H and L, and connect it with the bent lever O, O, by means of the bar N, which is riveted to the lever O, which lever multiplies the motion of the disk and thus renders a slight motion of the diaphragm sufficient. This lever extends in nearly a vertical direction from the bottom to the top of the instrument, being bent at right angles near the bottom, so as to pass below the parts G and J; it is then bent upward, and at this point there is attached a knife edge P P (similar to the bearing points in a common balance) which bears upon afulcrum Q. Near the top 'of the gage there is a spiral spring R, R, placed horizontally, having one end attached to a fixed hook S, the other being connected to the lever O, by the bar T. This spring resists the raising of the lever wit-h a force which increases as the lever is raised, and by this compensation counterbalances the variable pressure of the steam against the diaphragm and disk. A rack V, is jointed at one end U, to the lever O, and extends horizontally above the pinion IV, in the leaves of which it plays freely; the shaft of the pinion W is secured to the index X, which thus partakes of the motion of,the pinion. A guide Y is placed near the top r of the lever O,-to prevent it from vibrating laterally. The dial Z Z, is graduated for pounds avoirdupois pressure persquare inch, and each instrument is proved by a mercurial column, the length of the lever 0, between the bearing points and the tension of the spring being so adjusted as to insure perfect accuracy.

The pressure of steam, water or gas, acting upon the sheet of rubber I, causes it to bulge, and bear upon the disk M, which being connected with the bent lever O, by the bar N, the lever 0 also recedes a short distance, its mot-ion being checked by the spring R. Motion being'thus given to the lever O, the rack V, that is connected with the lever, plays horizontally in the pinion \V, and turns the index X. It will be observed that the contact of the disk M with the sheet rubber I, over a large part of the area that is exposed to the pressure, while the disk is at the same time held in contact with the rubber by the force of the spring, prevents the thin sheet rubber from being ruptured When the pressure is great notwithstanding it is thin so as to yield readily and be sensitive to slight changes of pressure, which Would be impossible if the sheet of rubber were thick enough to prevent rupture With- JOSEPH L. EASTMAN. 1,. 3.

1n presence of J M. BATCHELDER, F. L. BATCHELDER. 

